The present invention generally relates to machines for forming double packages, and particularly to forming blocks utilized in double package forming machines, and more particularly to forming blocks allowing ease of stripping of double packages from the forming machines, with the double packages being intact and of a consistent quality.
A common method of packaging cereals and other foodstuffs is a double package comprising a liner enclosed within a carton. In the past, such liners were formed of glassine or wax paper, however, the use of plastic liners has been increasing because of the advantages obtained thereover. Specifically, plastic liners provide a better moisture seal to the food stuffs being packaged providing extended freshness without staleness. Additionally, plastic liners have a greater tendency to prevent tearing or ripping. A further benefit obtained is that the liner is more consumer friendly allowing the liner to be opened without tearing or ripping and allowing the liner to be resealed by the consumer to preserve freshness. Further, the cost of plastic liners tends to be relatively less than the cost of prior glassine or wax paper liners.
However, one difference between plastic and prior glassine liners is that plastic is structurally more flimsy and has a greater tendency to collapse. Collapse of the liner may disrupt the proper functioning of the remaining packaging operations including but not limited to the filling of food stuffs into the liner, the dropping of coupons or premiums inside of the liner, closing and sealing the liner, and like operations. One major cause of liner collapse is problems in removing the double package from the forming block.
A typical method of forming a double package is to rotate a forming block through a series of steps where the liner and carton are formed on and then removed from the forming block. An example of a double package forming machine and its method of operation is set forth in U.S. Pat. No. 2,364,406 issued on Dec. 5, 1944 to J. G. Vergobbi. Specifically, the liner material is cut and wrapped around the forming block and the upper edges are sealed together, which in the case of plastic liners are fin sealed by sealing the two edges of the liner material in a face to face manner. Next, the bottom of the liner is sealed together, which in the case of plastic liners again is fin sealed.
After the side and bottom of the liner are sealed, a pattern of adhesive is applied to a flat blank for forming the carton. In the case of plastic liners where heat is not required to seal the liner, hot melt adhesive may be utilized. The blank is wrapped around the liner located on the forming block and the side flap is clamped down on the side of the blank. Next, the bottom flaps are tucked in and the bottom of the blank is clamped against the liner located on the forming block. Pressure may be applied to crease the bottom corners of the carton to form a more stackable, stable carton, to spread and adhere the adhesive, and in the case of cold adhesive to cure the adhesive. It can be appreciated that adhesive may be applied to the blank to not only form the carton but also to attach the liner to the carton. The formed carton and liner is then stripped from the forming block by reciprocating a stripper bar relative to the forming block along a longitudinal path from beyond the free end of the forming block to beyond the top edges of the carton, and then moving the stripper bar back to hook the free edges of the top flaps and pull the carton and liner from the forming block for transport to other packaging operations when the stripper bar is moved back to beyond the free end of the forming block.
In pulling the carton and liner from the forming block, a piston effect is created by the forming block as the carton and liner formed therein are withdrawn from the forming block. This piston effect creates a vacuum inside of the liner between the liner and the forming block. The vacuum force has a tendency to collapse the liner especially when the liner was formed of plastic which is more flimsy than glassine or other liner material. Prior to the present invention, compressed air was forced through tubes extending to the bottom of the forming block to fill the void created in the liner as the forming block moved out of the liner and the carton to assist the removal of the liner and carton from the forming block. It can be appreciated that the introduction of compressed air had to be exactly timed with the movement of the stripper bars. Such timing is difficult to obtain especially at the speed of operation of such double package forming machines where between 50 to 60 double packages are formed per minute.
Accordingly, in the development of machines for forming double packages and especially double packages including plastic liners, it is imperative that the forming blocks prevent the collapse of the liner as well as deliver consistent, quality double packages.
Thus, it is an object of the present invention to provide a novel forming block for double package forming machines, with the double package including a plastic liner in the preferred form.
Another object of the invention is to provide a novel forming block including provisions for providing communication of ambient air to the interior of the liner of the double package to offset the vacuum potentially created when the double package is stripped from the forming block.
Yet another object of the invention is to provide a novel hollow forming block allowing ambient air flow to the interior of the hollow forming block to adjacent the free end of the forming block and at a rate to prevent the creation of a vacuum when the double package is stripped from the forming block.
Still further, another object of the invention is to provide grooves on the periphery of the forming block for providing communication of ambient air between the liner of the double package and the periphery of the forming block.
In another aspect of the present invention, a further object is to provide the periphery grooves corresponding to the longitudinal path of the hooks of the stripper bars to allow movement of the stripper bars without engaging the forming block.